It's probably the fuel sender...it's built into the fuel filter in the gas tank IIRC.

 

As for the workarounds, you don't need to disconnect the battery for resetting the fuel gauge reading system.

There are two workarounds if you don't want to continue changing fuel pumps which come together with the senders.

1.- There is a fuse that you can inline with a switch to it, so that whenever you fill up your tank you just flip the switch and it will reset. The fuse is in the passenger compartment fuse box. You need to search on the old posts for the location details.

2.- The other is a connector in the driver's side rear wheel well, where if you diconnect the harness with the ignition off, and you wait a couple of seconds, then the fuel gauge mechanism will be reset.

Number one is more practical in my view.. On my former 2001 ML 320, I changed 3 fuel pumps and all develop sooner or later the gas gauge reading problem.

Even my brand new 2005 Ml 500 had the problem very early in life, around the first 2000 to 4000 miles. They fixed this one, though, by disabling how the gas left/averaging is calculated in the program. The side effect of this is that the gas reading is not uniform or linear as you may expect. This is more pronounced only when the tank is full. In my experience, when the tank is in the last quarter, it behaves much more uniformly.

AC

 

Thanks for the post about fuse #5

MY 2001 ML320 exhibited the fuel gauge problem today. I filled fuel this morning on my way to work. Soon thereafter, the fuel gauge showed that it was empty despite a complete fillup. I drove to my office, searched BenzWorld and discovered fuse 5 technique. Turned key to position 2, pulled out fuse 5 with nose pliers in the fusebox located near front passenger, waited 20 seconds, put fuse back, turned key to off position, waited a few seconds and turned engine on and voila.. fuel gauge functions again as normal!! Thanks Benzworld!!!

 

Mercedes like it even today, still selling fuel pump assembly for big $ instead of just the fuel sending unit by itself, FYI part No. A163 470 01 94 Some of them replaced under warranty, but very few compare to number of 163 MLs manufactured.
Mine is just not showing full on fillup, usually 3/4 or 7/8 max., in 3 years, I got used to it.
The sending unit potentiometer (variable resistor) wiper is exposed to fuel and acidity of the fuel will make coating or oxydation on the resistor surface in 1998-2001 MY.
Since 2001 I believe Mercedes installed resistance calibration circuit board to help the ECM to count fuel volume for trip computer.
I have a buletin for this printed out but I can't find it at this moment, I just remember that I had previously trouble to upload it into post so I scanned it and e-mailed it out to one of the forum members. I will try to find it and upload it.
Bernard

 

I think it was also around that time the fuel filter design was changed and that required
a modified pump design.

I did the filter update and put in a new OEM pump with updated lines. It lasted about 75k miles
and the sender did break. I could actually see where 2 tiny little contacts had broken off
sender at the swivel point where the contacts for the sender are located. Now on pump number
three now for about a year and hopefully it will hold up for awhile.

 

I never had one in my hands but I see the design with contacts exposed to fuel on picture (mine is still original with small filter at 168K miles). I have new upgrade filter and lines ready but truck is running fine and right now I have no spare time to play with it.
Bernard

 

but truck is running fine and right now I have no spare time to play with it.

You realize you just jinxed yourself.
Mike

 

FYI, I have found the bulletin:
DTB May 13, 2002 order # T-B-54.30/64 group 54
Subject: model 163.154/174/175 year 2001 and 2002
Fuel gauge accuracy
If you encounter instances in the above model vehicles where the fuel gauge reading is inaccurate, please perform the following procedure prior to replacing any components.
1. Remove fuse 5 in the RSE2 fuse holder.
2. Reinstall fuse 5 into the RSE2 fuse holder.
3. Instruct the customers not to fill the fuel tank untill they have reached the 1/2 tank level on the fuel gauge.
The fuel gauge reading for MY01 and MY02 vehicles have a virtual calculation performed on the first 19 liters (MY02) or 7 liters (MY01) of fuel. When the vehicle is filled prior to depleting the gas tank to these levels, an offset is calculated and stored in the instrument cluster memory. This is the cumulative affect and can result in the vehicle showing an empty tank even when actually full of fuel. The above procedure will remove any offset stored in the instrument cluster and return the fuel gauge to the correct accuracy.
This may help you out and sorry for my late respond.

 

That should work if the sender is not defective.

Based on the age of the vehicle if it is the original pump/sender unit it is probably a failure
and not a calibration issue.

 

Mine used to do this and I had to perform the removal of fuse #5, as stated in the above bulletin, several times over a one year period.

It has mysteriously and thankfully been fine for the past year or so now.

I hope I haven't jinxed myself Mike.

 

My gauge showed full at the last fill up but I doubt it will stay that way from now on.
Did anyone ever try to clean those contacts on sending unit for better accuracy of the gauge? I heard some of them corrode to the point of wiper end breaking off the float.
Is it possible for all of them to be jinxed?
Bernard

 

Same problem???

Hi to all.
My ML98 has a problem like this but don`t know if it's the same yours.
My fuel gauge shows full thank but it is really empty. How do i fix that?
Thaks

 

X18/3 connector inboard of left rear wheel has pin A (orange wire) and pin B (gray wire) comming from the level sending unit. At empty tank they should show 200 ohms, at full tank they should have 0.5 ohms of resistance. Disconnect this plug and turn the key on to see if the gauge needle will move (it should stay down at empty). Remove the key, check the resistance, your float may be stuck in upper position or these two wires are somehow shorted out.
Try to kick the fuel tank from below, this may break loose the stuck float lever.
Bernard

 

Thanks



Thanks for your help, i will try this solutions soon, and wil tell you the results.

 

One other trick that may avoid the need to continue reseting the gauge by pulling #5 fuse is to leave the ignition switch in position #2 during refueling. This appears to continue monitoring the fuel level and the gauge moves back to full as the gas is being added. This eliminates the need to hold your breath everytime you turn the key hoping your gauge will respond!

 

I have a 2002, and the answer is "both". The fuse 5 or wheel well connector trick works sometimes, but lately the behavior is more like an electrical intermittent--at some points in the range there's no signal and the gauge drops to zero. I've cleaned the wiper and contacts twice, and the last time I saw one of the contacts was missing.

I wouldn't be hard to replace the sender if there was such a thing as a good one to swap in!

 

With that contact missing the gauge will give you fits until the pump is swapped.
At least mine did. It lasted 10 years so I just bit the bullet and got a new pump.

 

I have an 03 with the same fuel gauge issue. Has anyone had success using the# 5 fuse trick or is there something else I need to do to fix this on the 03?
Ed

 

Mine is working perfect now, that is because I had to replace the fuel pump assembly.
When I checked the old pump, contacts on sending unit were dirty, coated with soot.

 

Bernard do you think it would work if you cleaned it and put it back?.

 

Fuel pump update - open hart surgery

Yes, it will.
But a bit of work have to be done to take the pump out.
I actually did that and put it back together but two days later my low fuel pressure problem came back, I could only do 35mph maximum. Sending unit and primary fuel filter built into pump are in first picture.
Here is my old fuel pump after cleaning, last picture is Pierburg fuel pump motor with bad (worn out) carbon brushes.

 

Fuel pump issue to the side for the moment, fuel sensor issues in the tank can often be recoevered using Stabil Blue (Marine Formula) in two tanks of gas over a 500 mile or so interval, the Stabil cleans up the fuel sensor in the tank... actually really good for that specific issue as well as prevents that specific issue.

 

Does anyone know where exactly Fuse #5 is in the RSE2 Fuse holder for a 2k ML55?

 

Here it is.

 

yet again 43sqd, thank you! :bowdown:

 

Hi:

I have a 2002 ML320, which has been experiencing the symptoms of the faulty fuel gauge.

I tried the workaround of unplugging the fuse.

When unplugged the fuel needle (and other controls) continued to show levels. They did not "fall to zero" like when you turn the car off. What DID happen is that the car would not turn on. The ignition worked but then it seemed as if the fuel pump was off because it would not start.

Is this what is supposed to happen when unplugging the correct fuse for the workaround?

After unplugging and reinserting the fuse, the car of course worked normally, but I did not see any material difference with the behavior of the fuel gauge.

Does that mean that the only solution is to change the sender (with fuel pump)?

Thanks

 

My fuel gauge is at times a little off. But what surprised me was if i use texaco fuel which in the uk is owned by chevron, may be wrong but i think i am right, contains techron as a fuel additive. If i fill my tank my fuel gauge starts working better without a shadow, and it does not take long. The expense kills me though.

 

Fuel gauge fixed with new gas cap

Had the same fuel gauge problem fixed in my 2001 ML320 when fuel pump was replaced for pump failure. After only 1-1/2 years with new pump, fuel gauge started doing the same thing again. Fuse 5 reset did not work anymore. Stumbled upon another thread stating it could be poorly sealing gas cap. So I cleaned gas cap seal and filler neck, and voila problem fixed, but shortly returned after weather cooled down (possibly gas cap seal contracting). So I bought a new gas cap thinking old gas cap seal was shot, and amazingly the problem is again fixed and so far staying fixed. I do notice the new gas cap is a lot harder to open so the fuel gauge problem may additionally be due to air leaking into the system due to a poor seal on the old gas cap. New OEM gas cap is only about $20 so worth a try before replacing sender/pump.

 

Poorly Fitting GasCap

Had the same fuel gauge problem fixed in my 2001 ML320 when fuel pump was replaced for pump failure. After only 1-1/2 years with new pump, fuel gauge started doing the same thing again. Fuse 5 reset did not work anymore. Stumbled upon another thread stating it could be poorly sealing gas cap. So I cleaned gas cap seal and filler neck, and voila problem fixed, but shortly returned after weather cooled down (possibly gas cap seal contracting). So I bought a new gas cap thinking old gas cap seal was shot, and amazingly the problem is again fixed and so far staying fixed. I do notice the new gas cap is a lot harder to open so the fuel gauge problem may additionally be due to air leaking into the system due to a poor seal on the old gas cap. New OEM gas cap is only about $20 so worth a try before replacing sender/pump.

Hi WestSanDiego! Did the poor fitting gas cap cause your Check Engine Light (CEL) to come on?